The shaft of an electric motor is generally supported and guided at the ends of the motor casing by two swivel bearings held by the motor casing, with the shaft being free to move axially through one of the bearings while being restrained axially relative to the other bearing by means of two resilient stops, thereby reducing play and vibration when the electric motor is in operation.
It has already been proposed to make said resilient stops by means of lock washers threaded over the shaft on either side of the swivel bearing, and by means of washers having a low coefficient of friction interposed between the lock washers and the bearing. In known manner, lock washers comprise a peripheral ring having claws or tabs which extend radially inwardly and slightly obliquely relative to the plane of the ring in such a manner as to grip the peripheral surface of the motor shaft. However, it has been observed that such washers, when thrust to abut against friction washers pressing against the bearing, tend to tilt relative to a plane perpendicular to the axis of the shaft and then do not exert uniform thrust on the washers. This causes the shaft and the rotor to vibrate longitudinally relative to the motor casing.
It has also been proposed to make the stops by means of flat rings or spring clips which are fixed to the shaft against both axial movement and rotational movement by engaging in grooves made in the shaft on either side of the bearing. Washers made of rubber or like material are interposed together with friction washers between the bearing and the flat rings.
However, there is sufficient dispersion in dimensions due to the motor shafts and the various washers being mass produced for the shaft to be correctly positioned relative to the bearing in some cases only, while in some other cases there is play between the washer and the stops on the shaft giving rise to vibration and noise, and in further other cases the stops are too tightly pressed against the bearing, giving rise to heating and to excessive wear of the friction washers while at the same time reducing the performance and the efficiency of the electric motor.
Preferred embodiments of the present invention avoid these various drawbacks.